Process Hazards Analysis (PHA)

ASSESMENT GUIDE
NAME
INSTITUTION
COURSE
DATE

Question 1
The purpose of the proof test is to detect dangerous concealed or hidden defects and failures in
a safety-related system such that if necessary, the system may be restored to a "new" state or a
similar practical condition as quickly as possible through a repair.
Proof Test Coverage (PTC) is the term that refers to the percentage of potentially dangerous
undetected failures uncovered by the procedures undertaken during the proof test.
Question 2
Process Hazards Analysis(PHA) is a systematic method of identification and evaluation of
dangers of specific industrial processes associated with highly dangerous chemicals so as to
prevent or control any related potential hazards.
Process Hazard Analysis is conducted by PHA team which consists at a minimum of a process
engineer, an operator, and a facilitator.
Question 3
a) Mean Time Before failure (MTBF) is the predicted time that a system takes from one
previous failure to the next failure when the system is under normal operation limits.
b) Failure rate (λ) is the inverse of the MTBF.
Failure rate (λ)= 1
MTBF
c) Mean Time to Repair (MTTR) is the amount of time required to repair a failed system
and restoring it to full functionality
d) A Test interval is the period between two proof tests that access the operational safety
of systems to ensure that they are free from failures or any defects.
e) The formula for PFDavg under perfect test coverage and constant failure rate is;
PFDavg =λD ×tce
Where
tce= λDU
λD ( T 1
2 + MRT ) + λDD
λD
MTTR
λDU = Dangerous Undetected Failure Rate (per hour)
λDD = Dangerous Detected Failure Rate (per hour)